Generally, the present invention is applicable to various communication systems. LTE (long term evolution) network evolving from UMTS (universal mobile telecommunications system) is explained as one example of the various communication systems, to which the present invention is applicable, in the following description.
FIG. 1 is a block diagram of LTE (long term evolution) network as a mobile communication system to which a related art or the present invention is applied.
The LTE network system has evolved from a conventional UMTS system. And, the 3GPP is working on the basic standardization of the LTE system.
An LTE network consists of a user equipment (hereinafter abbreviated UE), a base station (hereinafter abbreviated eNode B) and an access gateway (hereinafter abbreviated AG) located at an end of a network to be connected to an external network.
The AG includes a UPE (user plane entity) node responsible for a user traffic processing and an MME (mobility management entity) node responsible for a control. In this case, the MME and UPE nodes are able to communicate with each other via a new interface in-between.
At least one or more cells can exist in one eNode B. An interface X2 for a user or control traffic transmission is defined between the eNode Bs. And, an interface S1 is defined between the eNode B and the AG.
Layers of a radio interface protocol between a terminal and a network can be classified into L1 first layer), L2 (second layer0 and L3 (third layer) based on three lower layers of an open system interconnection (OSI) reference model widely known in communication systems. A physical layer belonging to the first layer provides an information transfer service using a physical channel. A radio resource control (hereinafter abbreviated RRC) layer located in the third layer plays a role in controlling radio resources between a terminal and a network. For this, the RRC layers enable RRC messages to be exchanged between the terminal and the network. The RRC layers can be distributed to network nodes including the eNode B, respectively. Instead, the RRC layer can be located at either the eNode B or the AG.
FIG. 2 is an architectural diagram of a radio interface protocol between UE (user equipment) and UTRAN (UMTS terrestrial radio access network) based on 3GPP radio access network specifications.
Referring to FIG. 2, a radio interface protocol vertically includes a physical layer, a data link layer, and a network layer and horizontally includes a user plane for data information transfer and a control plane for signaling transfer.
The protocol layers in FIG. 2 can be classified into L1 (first layer), L2 (second layer), and L3 (third layer) based on three lower layers of the open system interconnection (OSI) standard model widely known in the communications systems.
The respective layers of the radio protocol control plane shown in FIG. 2 and the radio protocol user plane shown in FIG. 3 are explained as follows.
First of all, the physical layer as the first layer offers an information transfer service to an upper layer using a physical channel. The physical layer is connected to a medium access control (hereinafter abbreviated MAC) layer above the physical layer via a transport channel. And, data are transferred between the medium access control layer and the physical layer via the transport channel. Moreover, data are transferred between different physical layers, and more particularly, between one physical layer of a transmitting side and the other physical layer of a receiving side via the physical channel.
The medium access control (hereinafter abbreviated MAC) layer of the second layer offers a service to a radio link control layer above the MAC layer via a logical channel. A radio link control (hereinafter abbreviated RLC) layer of the second layer supports reliable data transfer. A function of the RLC layer can be implemented by a function block within the MAC. In this case, the RLC layer may not exist. And, the MAC and RLC layers exist in an eNode B of a network.
A packet data convergence protocol (hereinafter abbreviated PDCP) layer of the second layer plays a header compression function to reduce an IP packet header size containing unnecessary control information having a relatively big size to enable efficient transmission of packets of IP such as IPv4 and IPv6. The PDCP layer exists in the AG of the network. The PDCP layer exists at an MME (mobility management entity) or the PDCP layers exist at the MME and a UPE (user plane entity), respectively.
A radio resource control (hereinafter abbreviated ‘RRC’) layer located in a highest part of the third layer is defined in the control plane only and is associated with configuration, reconfiguration and release of radio bearers to be responsible for controlling the logical, transport and physical channels (hereinafter, the radio bearer will be abbreviated RB). In this case, the RB means a service offered by the second layer for the data transfer between the UE and the UTRAN. And, the RRC layer in the network is located at the eNOde B.
As downlink transport channels carrying data to a UE from a network, there are a broadcast channel (BCH) carrying system information and a downlink shared channel (SCH) carrying a user traffic or control message.
And, the configuration of RB means a process of regulating characteristics of protocol layers and channels necessary for offering a specific service and a process of setting their specific parameters and operational methods, respectively. A traffic or control message of a downlink multicast or broadcast service can be transmitted via the downlink SCH or a separate multicast channel (MCH).
Moreover, as uplink transport channels carrying data from a UE to a network, there are RACH (random access channel) carrying an initial control message and an uplink SCH carrying a user traffic or control message.